The present invention relates to a spiral groove face seal, and more particularly to a spiral groove face seal in which an end face of a rotating sealing ring rotatable with a rotating shaft, and an end face of a stationary sealing ring facing the rotating sealing ring, form sealing surfaces for restricting fluid flow from a high pressure side to a low pressure side.
In general, a spiral groove face seal is used for sealing the space between a rotating shaft and a housing thereof. The spiral groove face seal is incorporated in, for example, gas turbines or compressors which generate high pressure.
Conventionally, an end face seal comprises two annular sealing rings facing each other, one of which includes a spiral groove area having a plurality of spiral grooves and a dam area extending from the spiral groove area and having a flat surface, and the other of which has a flat surface.
The end face seal of this type is disclosed in, for example, U.S. Pat. No. 4,212,475. In U.S. Pat. No. 4,212,475 spiral grooves are formed on a rotating sealing ring as shown in FIGS. 13 through 15. In FIGS. 13 through 15, a rotating shaft 1 accommodated in a housing 9 is provided with a sleeve 2. The sleeve 2 is connected to a rotating sealing ring 3 through a pin. A stationary sealing ring 4 is pressed against the rotating sealing ring 3 by the urging forces of springs 10 interposed between a sealing ring retainer 5 and a spring retainer 6. The rotating sealing ring 3 includes a spiral groove area 35 having a plurality of spiral grooves 33 and a dam area 34 extending from the spiral groove area 35 and having a flat surface. The spiral grooves 33 serve to pump fluid (gas) inwardly, and the dam area 34 serves to restrict fluid flow pumped by the spiral grooves 33.
Relative motion of the rotating sealing ring 3 and the stationary sealing ring 4 is caused by rotating the rotating shaft 1. Under dynamic conditions, the end face seal will be exposed to hydrostatic forces from fluid pressure and hydrodynamic forces from the spiral grooves 33. The spiral groove pattern pumps fluid (gas) inwardly to thereby form a fluid film on the sealing surfaces, whereby the rotating sealing ring 3 is brought out of contact with the stationary sealing ring 4. The leakage of fluid is restricted by keeping the gap between the sealing surfaces small.
On the other hand, another type of end face seal is disclosed in U.S. Pat. No. 3,499,653. In U.S. Pat. No. 3,499,653 the end face seal comprises a rotating sealing ring and a stationary sealing ring, as with the end face seal in FIGS. 13 through 15. One of the sealing rings has spiral grooves and a tapered surface to provide the necessary wedge-shaped space at the radially outer regions thereof.
In the end face seal of this type, when fluid enters into the wedge-shaped space between the rotating sealing ring and the stationary sealing ring, the sealing surfaces are forced out of contact by hydrostatic forces from fluid pressure. When the fluid is under low pressure, the sealing surfaces are not forced out of contact by only hydrostatic forces, but are also forced out of contact by hydrodynamic forces from the spiral grooves in addition to the hydrostatic forces.
However, in the end face seal disclosed in U.S. Pat. No. 4,212,475, a ridge portion (on which spiral grooves are not formed) on the spiral groove area 35 is located on the same plane as the dam area 34 as shown in FIGS. 13 through 15. Therefore, when starting the end face seal, the ridge portion and the dam area 34 of the rotating sealing ring 3 directly contact the surface of the stationary sealing ring 4. In this specification, this direct contact of two solid members is defined as "solid contact." As a result, fluid (gas) cannot enter between the contacting surfaces of the two sealing members, and a large quantity of starting torque is thus required due to a large quantity of sliding resistance when starting in such a state that fluid pressure is applied to the sealing rings. The same is true in the stationary sealing ring having spiral grooves.
On the other hand, the end face seal disclosed in U.S. Pat. No. 3,499,653 is a gap type hydrostatic mechanical seal so that the sealing surfaces are forced out of contact by hydrostatic forces from fluid pressure. Therefore, there is no problem in starting resistance at the time of starting. However, since the sealing surfaces are forced out of contact by hydrostatic forces of the fluid, fluid is leaked from the sealing surfaces having a certain gap when the machine incorporating the seal face is stopped.